Light Spectrum Effects on Metabolite Profile of Cannabis

As the FDA progresses toward a regulatory framework for hemp based cannabinoid products, I’ll touch on some unique research from the production side, focusing on lighting and hydration strategies in greenhouse settings and provide examples of how formulary might help drive the selection. Look for discussions on extraction methods or strain/chemovar choice at another time.

At a 2019 Cannabis Science Conference East talk, typical production methods for cannabis production were described as follows (Kern, 2019):

High light intensity and CO2 concentration

Photoperiod

Vegetative growth at 18 hours

Flowering < 12 hours

Use of Blue light during flowering

The blue light treatment is used to optimize several factors:

Increase terpenes with all blue light last three days of flower development

Blue light at end of day can increase leaf expansion increasing photosynthesis and plant mass yield

Research by Mosaleeyanon et al. (2005) showed that light impacts secondary metabolite production, with increased photosynthetic rates leading to increased total hypericin (hypericin + pseudohypericin) concentration in St. Johnswort.

Hawley et al. (2018) experimented with the use of subcanopy lighting (SCL) of red/blue (“Red-Blue”) or red-green-blue (“RGB”) light versus no SCL in a greenhouse production cannabis. They used a plant layout design to limit the amount of additional radiation from the subcanopy and to prevent the treatment light from influencing other plants. They ran the experiment without gyping (removal of the bottom 20 cm of stems). The SCL treatment created differences in the lower canopy metabolite concentrations:

From a QA perspective, the RB SCL treatment also provided the most consistent levels of cannabinoids and terpenes in both upper and lower canopy.

Hawely et al. (2018) suggested previous research (Miller et al., 1995: Zur et al., 2000) had demonstrated light spectra rich in green light was largely absorbed by terpenes, and that the plant had to up regulate the biosynthetic precursors in response to increased green light stimulus. The precursor molecules turn out to be part of both terpene and cannabinoid metabolic pathways, leading to an enriched biosynthetic stream. Greater precursors available led to increased production of both class of metabolites

Two examples of how formulary might take advantage of ecological influences

CBC and CBG concentrations have been shown to be present in leaves at equal or greater levels than in the flowers (Bernstein, Gorelick and Koch, 2019). This suggests that lighting and harvesting strategies may include adding leaf material to an extract and/or optimizing the impact of different light spectra on leaf metabolite profiles.Taking it a step further, cold water extraction of immature leaf of selectively bred cannabis chemotypes yields enriched CBC fraction (Potter, 2009)

Since CBC is the second most prevalent cannabinoid compound found in cannabis (Russo 2011), and research has shown topical anti-inflammatory activity (De Petrocellis et al., 2012: Cascio & Pertwee 2014; Oláh et al., 2016), and sebum reduction in acne, then leaf material might be combined with flowers in an extract. And the impact of under canopy lighting should also be investigated more extensively to determine if the leaf yield of cannabinoids and terpenes can be improved. Applying the RBC-SCL strategy to increase terpenes, the following enriched fractions might improve the results as an anti-acne topical: alpha-pinene as an effective antibacterial (Appendino et al., 2008); limonene, pinene and linalool decreasing sebum/sebocytes (Biro et al., 2009).

Experimenting with the yield in various chemovars based on multiple ecological inputs will make for a challenging project. The use of ecological inputs as one strategy for creating treatment specific strains might eventually be combined with chemovar selection and extraction protocols to create a highly specific therapeutic product.